Method for controlling air speed in a sterilizing tunnel during the heating of same tunnel

ABSTRACT

In a tunnel-like region of a sterilizing tunnel, containers are advanced by means of a conveyor device. For sterilization, a heated air flow oriented vertically in the region of the containers is used, which is generated by means of a fan and a heater. To prevent particles from being torn out of a sterile filter during the heating phase, there is a provision for adapting the rpm of the fan during the heating phase. According to the invention, this rpm adaptation is done by ascertaining the requisite rotary speeds of the fan beforehand at both room temperature and the sterilization temperature, whereupon a control unit of the sterilizing tunnel, on the basis of a predetermined functional relationship, raises the rpm of the fan as the temperature of the air flow is raised.

PRIOR ART

The invention is based on a method for controlling the air speed in asterilizing tunnel during its heating phase. Such sterilizing tunnelsare used particularly to sterilize ampules, vials or the like in thepharmaceutical packaging industry. Filter elements for cleaning the airrecirculated in the sterilizing tunnel are disposed in the sterilizingtunnels. So that the filter elements will on the one hand not be damagedbut on the other hand will have their optimal cleaning effect and sothat no particles will be torn out of the filter elements, it isnecessary that the flow through the filter elements be at a certain airspeed.

In a known method of this type, to attain a virtually constant air speedat various temperatures in the sterilizing tunnel during its heatingphase, speed measuring instruments are used, which are coupled via acontrol unit to a fan, whose rpm is varied in accordance with themeasured air speed. A disadvantage of this known method is that the airspeed measuring instruments, because of the high temperatures attainedin the sterilizing tunnel, such as 350° C. at the end of the heatingphase, have only a brief dwell time. Furthermore, because of theadditional measuring instruments and control units, the knownsterilizing tunnels are complicated in design. Measurement errors, forinstance from soiling of the measuring devices, also go undetected, sothat the sterilization process cannot be carried out reliably. This isbecause an incorrectly measured air speed also adjusts the rpm of thefan incorrectly, and so the filter elements fail to function optimally.

In another method, it is also known to set the fan rpm as constant, sothat at 350° C., for instance, it is 0.5 meters per second. To achievethis, however, an air speed of approximately 0.9 meters per second mustbe set when the sterilizing tunnel is cold. During the heating process,the initially set elevated air speed automatically decreases, because ofthe heating of the air, to the air speed required in the sterilization.At the beginning of the heating phase, however, because of the increasedair speed and the accordingly large quantity of air, the filter elementsdisposed in the intake or outlet region of the fan are burdened heavily.Furthermore, the fan must be designed to be strong enough for the largequantity of air. Thus once again, this method entails relatively higheffort and equipment expense.

ADVANTAGES OF THE INVENTION

The method of the invention for controlling the air speed in asterilizing tunnel during its heating phase, has the advantage over theprior art that it works without additional air speed measuringinstruments and at the same time is sufficiently precise, and the filterelements always function optimally. It follows from this that the fan orthe filters need not be made more powerful, and that the sterilizationprocess will function reliably. According to the invention, this isattained in that the fan rpm is varied in accordance with apredetermined function course.

Further advantages and advantageous refinements of the method of theinvention for controlling the air speed in a sterilizing tunnel duringits heating phase will become apparent from the claims and thedescription.

BRIEF DESCRIPTION OF THE DRAWING

One exemplary embodiment of the invention is shown in the drawing andwill be described in further detail below. The sole drawing figure showsa simplified cross section through a sterilizing tunnel.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The sterilizing tunnel 10 shown in FIG. 1 is used to handlepharmaceutical containers 11, such as ampules vials or the like, beforethey are filled. This requires that the containers 11, furnished innonsterile condition, be sterilized. This is done in the sterilizingtunnel 10 by introducing the containers 11, wet-cleaned beforehand, intothe sterilizing tunnel 10, in which, by means of a horizontallyrevolving, continuously driven conveyor belt 12, the containers arepreheated first, in an inlet region not shown, from room temperature toapproximately 40° C. Next, the containers 11 pass into the region of thehot area 13 shown in FIG. 1, in which the containers 11 are furtherheated to approximately 350° C.; germs and the like are killed by theheating and a hot air flow. Finally, the containers 11 are cooled downto room temperature again in a cooling area, also not shown, from whichthe containers are carried on to a filling system.

In the heating area 13, the sterilizing tunnel 10 has a tunnel-likeregion 14 with lateral boundary walls 15, in which the containers 11 aredisposed, standing upright on the conveyor belt 12. To replenish the hotair flow, an aspirating filter 17 is integrated into an opening in ahousing wall 16 of the sterilizing tunnel 10; this filter dischargesinto a conduit 18 disposed laterally from the region 14 and partitionedoff by the one boundary wall 15. A heater 20 is also provided in theconduit 18; the heater heats the aspirated air to the requisitesterilization temperature. From the heater 20, the air passes into avariable-speed fan 21, disposed above the region 14, that aspirates theair and conducts the air, heated in the heater 20, into the region 14 inthe form of a hot air flow oriented vertically from top to bottom, via asterile filter 23 disposed directly above the region 14. Below theconveyor belt 12, which is made of a special steel wire mesh and is thusair-permeable, a grid floor 24 is provided, below which an air exhaustregion 26 is disposed. The air exhaust region 26 discharges on the onehand into the conduit 18; on the other, via a second fan 27 in the inletregion of the sterilizing tunnel 10, some of the humid air is removed bysuction. To monitor the air temperature in the region 14, a temperaturesensor 29 is disposed above the containers 11 in a boundary wall 15; thetemperature sensor is connected to the control unit, not shown, of thesterilizing tunnel 10.

The sterilizing tunnel 10 described above functions as follows:

While the sterilizing tunnel 10 is being started up, the air in theregion 14 is heated by the heater 20 from room temperature to therequisite sterilization temperature, such as 350° C. In the process, theair is recirculated with the aid of the fan 21. To assure the optimalfunction of the sterile filter 23 during the sterilization, a flow speedof 0.5 m/s, for example, is needed, which requires a certain fan rpm.However, this fan rpm at room temperature would be equivalent to a flowspeed of the air of approximately 0.9 m/s, which is supposed to beavoided to prevent any particles from being torn out of the sterilefilter 23. For this reason, according to the invention, the fan rpm isascertained beforehand; at room temperature, it corresponds to a flowspeed of 0.5 m/s as well. This fan rpm, which is known to the controlunit of the sterilizing tunnel 10 as an initial or starting value, isbelow the requisite fan rpm, for the same flow speed of the air, at 350°C. During the heating phase of the sterilizing tunnel 10, the controlunit now constantly raises the fan rpm, so that during the heatingphase, over the entire temperature range, virtually the same flow speedprevails in the region 14.

In the simplest case, the fan rpm is raised either constantly or inincrements over the known or previously ascertained heating time.Preferably, however, the signal supplied to the control unit as aninitial value by temperature sensor 29 is used, on the basis of whichthe control unit raises the rpm, for instance via a linear relationship,as the temperature rises. The relationship between the temperature andthe requisite rotary speeds of the fan can, however, also be found onthe basis of a more-complex functional relationship stored in memory inthe control unit, for instance if flow resistances do not vary linearlywith the air temperature.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. A method for controlling the air speed in a sterilizingtunnel (10) during a heating phase, said sterilizing tunnel (10) havinga sterile filter (23) through which air flows, wherein said methodcomprises raising a rpm of a fan (21) from an initial value, at a firsttemperature that is below a sterilization temperature to a final valueat the sterilization temperature, so that the flow speed of the airthrough the sterile filter (23) during the temperature heating phase andfinal phase is virtually constant, in which the rpm of the fan (21) israised during the heating phase from the initial value, stored in memoryin a control unit, up to the final value on the basis of a predeterminedfunction.
 2. The method according to claim 1, in which the predeterminedfunction is a linear function.
 3. The method according to claim 2, inwhich the rpm of the fan (21) is varied, taking a temperatureascertained by a sensor (29) into account.
 4. The method according toclaim 2, in which the rpm of the fan (21) is varied, taking therequisite heating time into account.
 5. The method according to claim 1,in which the rpm of the fan (21) is varied, taking a temperatureascertained by a sensor (29) into account.
 6. The method according toclaim 1, in which the rpm of the fan (21) is varied, taking therequisite heating time into account.
 7. A method for controlling the airspeed in a sterilizing tunnel (10) during a heating phase, saidsterilizing tunnel (10) having a sterile filter (23) through which airflows, wherein said method comprises: sensing the temperature in thesterilizing tunnel during its heating phase, and in response to thesensed temperature controlling the rpm of a fan (21) from an initialvalue, when said sterilizing tunnel is at a first temperature that isbelow a sterilization temperature, to an rpm of a final value when thesterilizing tunnel is at the sterilization temperature, the rpm of thefan being controlled so that the flow speed of the air through thefilter during the heating phase is virtually constant and equal to theflow speed of the air when the sterilization tunnel is at itssterilization temperature.
 8. The method according to claim 7, in whichthe rpm of the fan is a linear function when compared to the sensedtemperature.
 9. The method according to claim 7, in which the rpm of thefan (21) is varied as a direct function of a temperature ascertained bya sensor (29).
 10. The method according to claim 7, in which the rpm ofthe fan (21) is varied as a direct function of the requisite heatingtime to heat the sterilization tunnel when starting at the sensedtemperature.